The invention is directed generally to improvements in MOS (metal oxide semiconductor) memories, and particularly to an improved bootstrap driver circuit for use in such memories.
MOS memories generally include row and column decoders, clock generators and a variety of buffers. At the heart of all such circuits are drivers which function essentially to receive a digital input signal to develop as rapidly as possible a strong output signal. Some such drivers include a capacitor in a regenerative feedback loop to "bootstrap" the output signal to its desired voltage level very rapidly.
One of the drawbacks of some prior "bootstrap" drivers is that their capacitors require a set-up time during which they are pre-charged after an input transition. Without such pre-charging, the bootstrapping effect will not occur. This effect is particularly evident when conventional bootstrap drivers are used in a fully asynchronous environment. In addition, the need for a set-up time has an adverse effect on the operating speed of the memory.
Further, conventional bootstrap drivers tend to be adversely affected by "glitches" (undesired voltage transients) received at their inputs. In some cases, a glitch may cause the pre-charge on the bootstrapping capacitor to be dissipated, thereby rendering the bootstrapping effect inoperative until the next cycle of pre-charge occurs.
Another drawback of prior bootstrap drivers is their tendency to consume an undesirably large amount of power. This effect is particularly disadvantageous where many of the memory's circuits are intended to be built using the same basic bootstrap driver configuration.
The problems mentioned above and other drawbacks associated with conventional bootstrap drivers have rendered them less than perfectly satisfactory, particularly for use in high speed, low power memories.